Isotactic polypropylene and ethylene/propylene copolymers are often used in the industry to produce articles such as fibers, films, molded parts and nonwoven fabrics. Additionally, blending these polymers with other polymers has also been the subject of past endeavors.
For example, U.S. Pat. No. 3,262,992 suggests the addition of a stereoblock copolymer of ethylene and propylene (having high crystalline melting points) to isotactic polypropylene leads to improved mechanical properties of the blend compared to isotactic polypropylene alone.
U.S. Pat. Nos. 3,853,969 and 3,378,606, suggest the formation of in situ blends of isotactic polypropylene and “stereo block” copolymers of propylene and another olefin of 2 to 12 carbon atoms, including ethylene and hexene.
U.S. Pat. No. 3,882,197 suggests blends of stereoregular propylene/alpha-olefin copolymers, stereoregular propylene, and ethylene copolymer rubbers.
U.S. Pat. No. 3,888,949 suggests the synthesis of blend compositions containing isotactic polypropylene and copolymers of propylene and an alpha-olefin, containing between 6-20 carbon atoms, which have improved elongation and tensile strength over either the copolymer or isotactic polypropylene. Copolymers of propylene and alpha-olefin are described wherein the alpha-olefin is hexene, octene or dodecene.
U.S. Pat. No. 4,461,872, discloses a blend produced in part by the use of another heterogeneous catalyst system which is expected to form copolymers which have statistically significant intramolecular and intermolecular compositional differences.
Two publications in the Journal of Macromolecules, 1989, volume 22, pages 3851-3866 describe blends of isotactic polypropylene and partially atactic polypropylene which purportedly have desirable tensile elongation properties.
U.S. Pat. Nos. 5,723,217; 5,726,103; 5,736,465; 5,763,080; and 6,010,588 suggest several metallocene catalyzed processes to make polypropylene to produce fibers and fabric. U.S. Pat. No. 5,891,814, discloses a dual metallocene-generated propylene polymer used to make spunbond fibers. WO 99/19547 discloses a method for producing spunbonded fibers and fabric derived from a blend of a propylene homopolymer and a copolymer of polypropylene.
U.S. Pat. No. 6,342,565 and its equivalent WO 00/070134 disclose, at Table 4, column 24, fibers comprising 80, 90, and 95 weight % of Achieve 3854 and 20, 10 and 5 weight %, respectively of a propylene/ethylene copolymer having 13.5% ethylene and an ML of 12. These particular blends are not made into films, molded articles or non-woven materials. The fibers in Table 4 are reported to be inelastic and are unsuitable in the elastic applications desired in U.S. Pat. No. 6,342,565.
U.S. Pat. Nos. 6,525,157; 5,504,172; and WO 00/01745 disclose various propylene/ethylene copolymers. US 2003/0130430 discloses blends of two different propylene/ethylene copolymers. U.S. Pat. No. 6,642,316, WO00/070134, WO 00/01766, U.S. Pat. Nos. 6,500,563; 6,342,565, 6,500,563 and WO 00/69963 disclose elastic blends of crystalline polypropylene and propylene/ethylene copolymers. U.S. Pat. No. 6,153,703 discloses blends of semicrystalline copolymers and propylene ethylene polymers having very high toughness without loss in modulus. EP 0 629 632 and EP 0 629 631 disclose blends of polypropylene and ethylene-propylene copolymers having certain triad tacticities and proportions of inversely inserted propylene units.
U.S. Pat. No. 6,635,715 and its equivalents EP 1 003 814 B1 and WO 99/07788 disclose blends of polypropylene and Escorene 4292 with propylene/ethylene copolymers for use as thermoplastic elastomers.
EP 0 374 695 A1 discloses visually homogeneous blends of an ethylene-propylene copolymer and Profax™ 6331 by Basell.
U.S. Pat. No. 6,750,284 discloses thermoplastic membranes comprising propylene-ethylene copolymers and up to 40 wt % polypropylene.
WO 03/040095, WO 03/040201, WO 03/040233, and WO 03/040442 disclose various propylene-ethylene copolymers made with non-metallocene catalyst compounds. WO 03/040202 discloses films and sealants made from the propylene-ethylene copolymers made with non-metallocene catalyst compounds.
Additional references of interest include WO 94/28042, EP 1 002 814, WO 00/69965, WO 01/48034, WO04035681A2, EP 0 400 333 B1, EP 0 373 660 B1, WO04060994A1, U.S. Pat. Nos. 5,453,318, 5,298,561, and 5,331,047.
This invention is also related to copending U.S. application Ser. No. 10/402,275 filed Mar. 28, 2003.
However, none of the above disclose heterogeneous blends having a balanced set of properties comprising toughness (down to 0° C.), flexibility and clarity while still maintaining good crystallizability for convenient fabrication under polypropylene conditions. Further it is desirable to provide molded articles that show little or no stress whitening.